Pseudomonas aeruginosa infection is a particularly important problem in patients with cystic fibrosis. More than 70% of patients with cystic fibrosis harbor P. aeruginosa in their lungs and up to 90% of cystic fibrosis patients who survive to adulthood have chronic obstructive bronchitis associated with P. aeruginosa.
Most of the strains of Pseudomonas isolated from patients with cystic fibrosis produce a peculiar exopolysaccharide that is antigenic and has been characterized as an alginic acid. Production of the exopolysaccharide is observed only among one or two percent of pathogenic Pseudomonas strains isolated from patients without cystic fibrosis. These so-called "mucoid" Pseudomonas strains are considered virtual markers of cystic fibrosis when isolated from a patient with bronchitis.
The exopolysaccharide is believed to contribute to the persistence of the mucoid-generating Pseudomonas strains in the lungs of cystic fibrosis patients. The exopolysaccharide of Pseudomonas aeruginosa has, however, been extracted and an exopolysaccharide vaccine capable of inducing an immune response against multiple strains of Pseudomonas has been developed. See Pier, U.S. Pat. No. 4,578,458, the entire contents of which are incorporated herein by reference.
It has been shown that this particular exopolysaccharide, referred to hereinafter as "MEP" antigen, elicits in mice antibodies capable of facilitating opsonization of mucoid Pseudomonas aeruginosa, thereby resulting in bacterial death. Nevertheless, these so-called "opsonizing" antibodies are best produced only when certain forms of the MEP is used to immunize mice. Administration of most preparations of MEP at high dosages elicits nonopsonizing antibodies.
In humans, opsonizing antibodies are clearly associated with resistance to mucoid P. aeruginosa infection. However, it is difficult to provoke production of opsonizing antibodies in humans by immunizing them with alginic acid-like MEP. One exception is when humans are given 100 .mu.g doses of the largest-sized polymers of MEP. Although induction of opsonizing antibodies is the goal of any MEP vaccine, it would be useful to develop antibodies against Pseudomonas aeruginosa that will be opsonizing at all dosage levels and regardless of the size of the particular alginic acid/MEP antigen.
Native MEP alginic acid antigens are composed of a uronic acid polymer backbone, made up of D-mannuronic acid and L-guluronic acid linked together in a beta- 1, 4 linkage. The .polymer backbone carries hydroxyl groups, some of which are derivatized but only with acetic acid. Although both D-mannuronic and L-guluronic acids have hydroxyl groups, acetylation occurs only on the hydroxyl groups of the D-mannuronic acid moieties in native MEP. The hydroxyl groups of the L-guluronic acid are free of acetylation. The degree of acetylation of the native MEP is typically between 2 and 12% by weight, although extremes have been reported where the acetylation is below 2% by weight and up to about 19% by weight in some strains. None are believed optimal for eliciting opsonizing antibodies.
There is no acetylation or short chain carboxylic acid derivatization of seaweed alginic acid.